Keil had a good 8051 book on their demo CDROM, along with just about every chip data sheet and vendors' apnotes. This book, "The Final Word on the 8051" is 255 pages long, and covers the 8051 and C programming for it.

I would expect the book to also be available on their website. I believe Andy Neil put up a link to it recently, you might try Search.

Dennis